1. Field of the Invention
This invention relates to a vehicle of the so called off-road type. More particularly, this invention relates to an improved hydrostatic drive system that can be employed for motive power for the off-road vehicle and provide a wide range of sensitivity and speed options for the operator.
2. Description of the Prior Art
A wide variety of off-road type vehicles have been known in the prior art. Each type of vehicle has been expensive and not used fully, since it was ordinarily connected with a particular type of attachment. As described in my co-pending application entitled "Adaptable Combination of Vehicle and Attachments", Ser. No. 919,179, filed June 26, 1978, now U.S. Pat. No. 4,222,186, there is provided an adaptable expensive vehicle that can be used with a wide variety of attachments such as augers, dump beds, ditch digging equipment, back hoes, revolving jib cranes, fork lifts and the like to more fully utilitize the vehicle. In my co-pending application entitled "Off-road Vehicle that both Oscillates and Articulates," Ser. No. 934,586, filed Aug. 17, 1978, there was described improvement in which the vehicle both oscillated and articulated to afford a high degree of maneuverability, ease of steering and provide a substantially level platform for operation of the attachments. In my co-pending application entitled "Hydrostatic System with Over-Control Compensation," Ser. No. 950,404, filed Oct. 11, 1978 now U.S. Pat. No. 4,215,547, there was disclosed an improved hydrostatic drive system in which over control compensation was provided by means for moving an actuating member back toward a neutral position. The descriptive matter of all these applications are incorporated herein by reference for details that are omitted herefrom. These inventions represent significant advances in the art but still fail to provide totally satisfactory off-road vehicle with a hydrostatic drive system, since there was a propensity to over control such that the operator could not easily control the vehicle in rough terrain or the like if operating at the high speeds commensurate with traveling a relatively smooth road or open path.
The prior art has seen the development of other attempts to provide this sensitivity. U.S. patents such as the following illustrate the state of the art technology. U.S. Pat. No. 3,237,478 discloses an accelerator linkage including a motion cancelling mechanism so as to allow relative movement between the chassis and the vehicle motor without "hunting" of engine speeds. U.S. Pat. No. 3,316,773 describes foot and hand levers for neutral, forward and reverse positions and for various pump displacements therewithin. The hand control establishes forward and reverse ranges but not sensitivity. One of the more important patents is U.S. Pat. No. 3,525,266 which provides variable speed ranges for forward and reverse accelerator pedals but is a more complex invention that ensures that the transmission is in neutral when it is supposed to be. The disclosed invention has a link to determine the speed ratio of the transmission. U.S. Pat. No. 3,535,951 describes a hand lever for setting the primary or minimum speeds; a foot override is provided; but counterweights and shock absorbers prevent temporary overriding from lowering the hand lever setting upon rebound as in the prior art. U.S. Pat. No. 3,537,328 describes hand and foot controls wherein the hand control in neutral and the foot control in forward position will cause an advance at a speed proportional to a degree of movement of the pedal. The foot pedal also increases and decreases the speed of the hand setting. U.S. Pat. No. 3,541,878 automatically sets the neutral position. A spring opposes the manual setting to resist the tendency to increase the speed in a given direction.
From the foregoing, it can be seen that the prior art has not been totally satisfactory in providing a simple, economical sensitivity control on a hydrostatic system having a pump driving a variable displacement pump with an actuating member driving an actuatable device. More specifically, the prior art has not been satisfactory in providing an off-road vehicle driven by hydrostatic system in which a one or more variable displacement pumps drive constant displacement wheel motors and in which the operator can select sensitivity for the particular terrain or operating conditions.